The development of numerical representations plays a central role in a child’s mathematical abilities. Previous studies have reported that children’s numerical representations shift from logarithmic to linear ones and the slope of linear representation shifts from 0 to 1. In order to investigate the developmental process in detail, we carried out a longitudinal study. Thirty young preschoolers (mean age = 4 years, 1 month) and 47 middle preschoolers (mean age = 5 years, 1 month) received a number-to-position task (0-10) twice over nine months. According to our results, both groups were most suitable linear representations, but the slope of middle preschoolers’ performance was nearer 1 than the young preschoolers’ performance. However, the slopes of both groups were not much different when we divided the children in fitted or non-fitted function. For this reason, previous studies could not properly evaluate the development of slope. It is possible that the non-fitted representations are transformed into linear representations with slope away from 1 partly through logarithmic representations.本論文のデータの一部は，日本心理学会第79回大会において発表したものである。